Treatment of gas well production wastewaters

ABSTRACT

A method of treating a wastewater is provided and can be used, for example, to treat a gas well production wastewater to form a wastewater brine. The method can involve crystallizing sodium chloride by evaporation of the wastewater brine with concurrent production of a liquor comprising calcium chloride solution. Bromine and lithium can also be recovered from the liquor in accordance with the teachings of the present invention. Various metal sulfates, such as barium sulfate and strontium sulfate, can be removed from the wastewater in the production of the wastewater brine. Sources of wastewater can include gas well production wastewater and hydrofracture flowback wastewater.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/222,481, filed Aug. 31, 2011, which issued asU.S. Pat. No. 8,877,690 B2 on Nov. 4, 2014, both of which areincorporated herein in their entireties by reference.

FIELD

The present teachings relate to methods for treating wastewater, andmore specifically, methods for treating gas well hydrofracture andproduction wastewaters.

BACKGROUND

While various individual methods are available for addressing specificconstituents of gas well wastewaters and for treatment of abandoned coalmine acid drainage (AMD), there exists no process to treat, or co-treat,such wastewaters in a manner that renders such wastewaters suitable forrecycle or reuse.

The drilling of natural gas wells and subsequent on-going recoveryand/or production of natural gas produces a number of wastewater streamscommonly identified as completion, hydrofracture flowback, andproduction waters. Drilling of a gas well also requires a substantialamount of water for makeup of the virgin, prior to use, drilling muds,completion, and hydrofracture waters. It is estimated that a typicaldeep horizontal gas well requires from 3 to 10 million gallons ofhydrofracture water for completion/hydrofracture and generates an equalamount of hydrofracture flowback and production wastewaters.Hydrofracture flowback, generally 10 to 25% of the hydrofracture watervolume, is now commonly filtered, diluted with fresh water, and reusedfor makeup of hydrofracture water. Production wastewater is contained inthe produced gas and a typical gas well will produce from 100 to 4,000gallons per day for the production life of the gas well.

With significant new large drilling activities linked to tight gas shaleformations such as the Marcellus Shale in Pennsylvania, the provision ofsufficient water for new drilling activities and subsequent disposal oflarge volumes of wastewater has become a critical issue. The wastewatersproduced by gas well drilling, completion, and production activitiespresent some unusual and difficult problems with regard to treatmentsuitable to enable disposal by discharge to surface waters.

Recent disposal activities have included co-treatment in publicly ownedtreatment plants (POTW), the use of industrial treatment systems, andthe use of a limited number of purpose built treatment plants. Thesemethods of disposal all treat and discharge treated wastewater tosurface waters but are capable of removing only a limited number andamount of the pollutants typically present. POTW are limited in that theamount of wastewater that can be treated is limited by the bariumcontent, which can affect the production of a sludge characterized as ahazardous waste. Other processes are limited in that they cannot obtaina substantial reduction in dissolved solids.

In 2008, the Monongahela River in Western Pennsylvania experienced arapid rise in dissolved solids content which severely disrupted manypublic water supplies and industrial operations. The cause was found tobe the discharge of gas well wastewaters treated by many POTW situatedalong the river.

The regulatory agency, Pennsylvania Department of EnvironmentalProtection, (PADEP) subsequently placed a very restrictive limit of 500mg/l on dissolved solids discharges to surface waters resulting fromtreatment of gas well wastewaters. This limit went into effect on Jan.1, 2011, for all new dischargers with a starting discharge date of Apr.11, 2009.

Table 1 below shows analytical data on a typical hydrofracture flowbackwastewater. As can be seen, it is extremely high in dissolved solids,toxic barium, and scale formers such as calcium, iron, magnesium, andstrontium.

TABLE 1 Parameter Analytical Result conductivity - mmhos 152,000dissolved solids - mg/l 175,268 total suspended solids - mg/l 416biological oxygen demand, 5 day - mg/l 489 methyl blue activesubstances - mg/l 0.939 chloride - mg/l 73,370 oil/grease - mg/l 38total organic carbon - mg/l 114.5 ammonia-N - mg/l 83.5 chemical oxygendemand - mg/l 600 total hardness - mg/l 39,100 strontium - mg/l 6,830barium - mg/l 3,310 calcium - mg/l 14,100 iron - mg/l 52.5 magnesium -mg/l 938 manganese - mg/l 5.17

In addition to these major constituents, low levels of bromide, lithium,copper, nickel, zinc, lead, and other assorted heavy metals are alsocommon.

With the development of means to simply filter hydrofracture flowbackfor immediate reuse as hydrofracture makeup waters, the remaining majorproblem presented by development of the Marcellus gas field is theproduction wastewater. As shown by the following analytical data on atypical production wastewater, it is extremely high in dissolved solids,toxic barium, and other elements such as calcium, magnesium, andstrontium, for example, as shown in Table 2 below.

TABLE 2 Parameter Analytical Result dissolved solids - mg/l 202,690chloride - mg/l 180,000 ammonia-N - mg/l 132.2 strontium - mg/l 3,600barium - mg/l 6,000 calcium - mg/l 17,500 iron - mg/l 100 magnesium -mg/l 1,800 manganese - mg/l 3.5 sodium mg/l 80,000 lithium mg/l 189bromide mg/l 812Trace levels of radioactives, such as uranium and radium, are alsopresent as well as lead.

The only known technology for treatment of such a wastewater to meet thecurrent PADEP dissolved solids limit for surface water discharge isevaporation. Prior to evaporation, the toxic barium would have to beremoved to prevent the resultant dry salt cake from being a hazardouswaste while the scale formers calcium, magnesium, iron, and strontiumwould have to be removed to prevent scale formation on heat transfersurfaces.

An alternative to trying to treat for surface water discharge, orpretreat and evaporate, would be to treat the wastewater for recycle ashydrofracture makeup water. From various sources in the gas wellhydrofracture service industry, it appears that the specific parametersshown in Table 3 below would be required of water to be used for makeupof hydrofracture water.

TABLE 3 Parameter Recommended Values Scale Ions - aluminum, barium,maximum of 2,500 mg/l as CaCO3 calcium, iron, magnesium, manganese, andstrontium Dissolved Solids maximum of 50,000 mg/l Iron maximum of 20mg/l Suspended Solids none Calcium maximum 350 mg/l as CaCO3

The makeup water would need to be substantially free of microorganismsto prevent growth of microorganisms in the fractured gas bearing strata.

There is currently no known technology for treatment of such awastewater to comply with current PADEP dissolved solids limit forsurface water discharge. Simple evaporation to reduce the liquid to asolid is not a viable method due to the presence of toxic barium, whichrenders the produced solid a “hazardous” waste, making disposalextremely costly. While the toxic barium can be removed by theSequential Precipitation process taught in U.S. Pat. No. 8,834,726 B2,which is incorporated herein in its entirety by reference, evaporationof the remaining liquid results in production of a mixed calcium,magnesium, and sodium chloride salt, which is highly deliquescent andcannot be disposed of by landfill.

The sole current alternative is to treat the production wastewater forrecycle as hydrofracture makeup water. That process is sequentialprecipitation and is described in U.S. Pat. No. 8,834,726 B2.Unfortunately, production wastewater will be generated in volumes farexceeding the needs for hydrofracture makeup water considering thatproducing gas fields do not require further hydrofracture, other than onan infrequent basis with intervals measured in tens of years. A secondproblem with this process is that the calcium and magnesium are removedfrom the wastewater as calcium carbonate and magnesium hydroxiderespectively producing large amounts of a low value product, calciumcarbonate or limestone, and consuming large amounts of an expensivereactant, sodium carbonate.

Moreover, the pre-treatment of gas and oil well wastewater utilizingdual channel oil and a solids separator must be designed to AmericanPetroleum Institute standards and is required to remove gross solids andfree hydrocarbons from the wastewater prior to further processing. Thepresent invention addresses these requirements.

SUMMARY

To address these and other problems, the present teachings provide afractional crystallization process wherein brine produced in a firstbarium removal step such as that described in U.S. Pat. No. 8,834,726B2, can be further treated by evaporation to the point where sodiumchloride almost completely fractionally crystallizes from the liquor. Noadditional costly reagents are required and the produced calciumchloride solution, crystalline sodium chloride, and distilled water arecurrent commodities. The present teachings can provide a completeprocess, equipment, and chemical additions, required to treat gas wellproduction wastewater with complete resource recovery, eliminating theneed for any disposal of sludge or non-compliant waters.

According to various embodiments of the present invention, a method oftreating a gas well hydrofracture flowback and/or production wastewater(production wastewater) is provided that comprises recycling slurry ofbarite sludge and wastewater brine for further precipitation of bariumsulfate, before separating the barite sludge from the brine. The methodcomprises contacting a production wastewater containing barium, with asource of sulfate ions, in a first tank and under conditions toprecipitate barium sulfate. The contacting can comprise adding fromabout 100% to about 150% of a stoichiometrically equivalent amount ofsulfate ions to the first tank, based on the amount of barium ions inthe first tank. Barium sulfate can then be precipitated from theproduction wastewater in the first tank to form a slurry of precipitatedbarium sulfate and a wastewater brine. The wastewater brine can comprisesodium, magnesium, strontium, and calcium chlorides. The slurry is thenpumped or otherwise moved to a second tank. In the second tank, theslurry can be mixed with a second reagent, for example, a pH-adjustingreagent such as sodium hydroxide. Optionally, slurry can then be pumpedor otherwise moved to a third tank wherein the slurry can be mixed witha third agent or reagent, for example, a flocculating agent. The treatedslurry can then be recycled by being pumped or otherwise moved back tothe first tank, and the precipitating, pH-adjusting, and optionalflocculation can be repeated one or more times to form a refinedwastewater brine.

The method can further comprise evaporating the refined wastewater brineto form water and evaporation products, for example, evaporationproducts comprising crystalline sodium chloride. The evaporating canfurther comprise forming a liquor comprising from about 25% by weight toabout 60% by weight calcium chloride based on the total weight of theliquor. The method can further comprise adjusting the pH of the refinedwastewater brine to be between 6.5 and 7.5, before the evaporating. Themethod can further comprise filtering the evaporation product to form aretentate comprising crystalline sodium chloride, and a filtratecomprising the liquor, after which the retentate can be washed withsaturated sodium chloride brine and dried. The method can furthercomprise cooling the evaporation product prior to the filtering. Themethod can further comprise measuring the specific gravity of thefiltrate, and if the specific gravity is not high enough, the filtratecan be further processed, for example, by further evaporating, until adesired specific gravity is achieved.

In some embodiments, the method can further comprise moving the refinedwastewater brine to a fourth mixing tank and adding from about 100% toabout 150% of a stoichiometrically equivalent amount of sulfate ions tothe fourth mixing tank, based on the amount of strontium ions in thefourth mixing tank. Strontium sulfate can then be precipitated in thefourth mixing tank. The method can further comprise recovering anddrying the precipitated strontium sulfate. If flocculation is omittedfrom the method, then the fourth mixing tank can instead be a thirdmixing tank.

According to various embodiments of the present invention, a method oftreating a gas well hydrofracture flowback and/or production wastewater(production wastewater) is provided that comprises first precipitatingand recovering barium sulfate and subsequently precipitating andrecovering strontium sulfate. The method can comprise contacting aproduction wastewater containing barium, with a source of sulfate ions,in a first tank and under conditions to precipitate barium sulfate. Thecontacting can comprise adding from about 100% to about 150% of astoichiometrically equivalent amount of sulfate ions to the first tank,based on the amount of barium ions in the first tank. Barium sulfate canthen be precipitated from the production wastewater in the first tank toform a slurry of precipitated barium sulfate and a wastewater brine. Thewastewater brine comprises strontium chloride and can also comprisesodium, magnesium, and calcium chlorides. The slurry can then be pumpedor otherwise moved to a second tank wherein the slurry can be mixed witha pH-adjusting reagent, for example, to increase the pH of the slurry.Sodium hydroxide can be used as the pH-adjusting reagent. Precipitatedbarium sulfate can then be removed from the slurry to form a separatedwastewater brine. The separated wastewater brine can then be pumped orotherwise moved to a third tank. In the third tank, the separatedwastewater brine can be contacted with a source of sulfate ions underconditions to precipitate strontium sulfate. Strontium sulfate can thenbe precipitated from the separated wastewater brine in the third tank,and recovered. The method can further comprise removing precipitatedstrontium sulfate from the separated wastewater brine to form a refinedwastewater brine, and evaporating the refined wastewater brine to formwater and evaporation products. The evaporation products can comprise,for example, crystalline sodium chloride. In some embodiments, the pH ofthe refined wastewater brine can be adjusted to be between 6.5 and 7.5,before the evaporating.

The method can optionally further comprise flocculating the bariumsulfate slurry after mixing it with the pH-adjusting reagent in thesecond tank and before removing the precipitated barium sulfate.

In some cases, the method can further comprise moving the refinedwastewater brine to a third tank and adding from about 100% to about150% of a stoichiometrically equivalent amount of sulfate ions to thethird tank, based on the amount of strontium ions in the third tank.Strontium sulfate can then be precipitated in the third tank. As withother methods of the present invention, the method can further compriseadding an oxidizing agent, such as potassium permanganate, to the firsttank while contacting the production wastewater with the source ofsulfate ions.

In yet other various embodiments of the present invention, a method oftreating a gas well hydrofracture flowback and/or production wastewater(production wastewater) is provided that produces a salable, liquidslurry of barite sludge. The method can comprise contacting a productionwastewater comprising barium, with a source of sulfate ions, in a firsttank and under conditions to precipitate barium sulfate. Barium sulfatecan then be precipitated from the production wastewater in the firsttank to form a slurry of precipitated barium sulfate and a wastewaterbrine. The wastewater brine can comprise sodium, magnesium, strontium,and calcium chlorides. The slurry can then be pumped or otherwise movedto a second tank wherein it can be mixed with a pH-adjusting reagent,for example, to increase the pH of the slurry. Sodium hydroxide can beused as the pH-adjusting reagent. The precipitated barium sulfate canthen be removed or otherwise recovered from the slurry, in the form of abarite sludge. The barite sludge can then be concentrated, for example,in a thickener. The barite sludge can then be stabilized and pH-adjustedto increase the pH of the barite sludge. The stabilizing can compriseadding calcium lignin sulfonate, polyacrylate, another polymer, or acombination thereof, to the barite sludge. After the concentrating, thestabilizing, and the pH adjustment, the resulting barite sludge can bein the form of a liquid slurry, and the method can further comprisepackaging the liquid slurry in a storage tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are the top and bottom, respectively, of a schematicflow diagram of an exemplary wastewater treatment system according tovarious embodiments of the present teachings, wherein flow line X shownin FIG. 1A is a continuation of flow line X shown in FIG. 1B, flow lineY shown in FIG. 1A is a continuation of flow line Y shown in FIG. 1B,and flow line Z shown in FIG. 1A is a continuation of flow line Z shownin FIG. 1B.

FIGS. 2A-2D constitute a schematic flow diagram of an exemplarywastewater treatment system according to various embodiments of thepresent teachings, wherein flow lines A-C shown in FIG. 2C arecontinuations of flow lines A-C, respectively, shown in FIG. 2A, flowlines S-W shown in FIG. 2B are continuations of flow lines S-W,respectively, shown in FIG. 2A, flow lines D-J shown in FIG. 2D arecontinuations of flow lines D-J, respectively, shown in FIG. 2B, andflow lines X-Z shown in FIG. 2D are continuations of flow lines X-Z,respectively, shown in FIG. 2C.

FIGS. 3A-3C constitute a schematic flow diagram of another exemplarywastewater treatment system according to various embodiments of thepresent teachings, wherein flow lines X and Y shown in FIG. 3B arecontinuations of flow lines X and Y, respectively, shown in FIG. 3A,flow line Z shown in FIG. 3C is a continuation of flow line Z shown inFIG. 3A, and flow lines A, B, C, D, and E shown in FIG. 3C arecontinuations of flow lines A, B, C, D, and E, respectively, shown inFIG. 3B.

FIG. 4 is a schematic flow diagram of a wastewater treatment sub-systemaccording to various embodiments of the present teachings, forrecovering a strontium sulfate sludge and/or for removing strontium andproviding a low strontium-content calcium chloride product.

DETAILED DESCRIPTION

According to various embodiments of the present teachings, a process forthe treatment of hydrofracture wastewaters, for example, productionwastewater, is provided to meet the specific parameters discussed above.The method is suitable for either direct reuse or for reuse followingaddition of low dissolved solids water. Furthermore, to address concernsregarding depletion of the fresh water supply in the Marcellus shaledevelopment area, the present teachings provide for the co-treatment ofhydrofracture flowback and production wastewaters with abandoned coalmine acid drainage (AMD). Such co-treatment puts to good use a pollutedwater source and provides a reduction of dissolved solids content in thetreated water.

According to various embodiments of the present teachings, a method oftreating a wastewater is provided that comprises contacting ametal-containing wastewater with a source of sulfate ions andprecipitating metal compounds from the wastewater in the form of one ormore metal sulfates. For example, barium can be removed as bariumsulfate. The one or more metal sulfates can then be removed from thestream of wastewater to form a first treated wastewater. The firsttreated wastewater can then be contacted with a source of carbonate ionsand the method can comprise precipitating one or more metal carbonatesand/or hydroxides from the treated wastewater after contact with thesource of carbonate ions. The resultant mixture can comprise a secondtreated wastewater and one or more metal carbonates. The mixture canthen be contacted with a source of hydroxide ions and the method cancomprise precipitating one or more metal hydroxides from the secondtreated wastewater. In some embodiments, the method can further compriseremoving other metal sulfates such as strontium sulfate, andprecipitated metal carbonates and/or metal hydroxides from the mixture,for example, removing calcium carbonate, strontium carbonate, strontiumhydroxide, and magnesium hydroxide.

According to various embodiments of the present teachings, aftermetal-containing wastewater is contacted with a source of sulfate ions,the resulting wastewater can be contacted with an anionic polymer in anamount sufficient to flocculate the one or more metal sulfates. Theflocculated metal sulfates can then be removed from the wastewater. Insome embodiments, the metal-containing wastewater can comprise bariumand the process can comprise producing one or more barium sulfates thatcan then be removed from the wastewater. Sufficient sulfate ions can beused to precipitate at least 90% of the barium from the metal-containingwastewater. In some embodiments, the method can further comprisecontacting a mixture of treated wastewater and one or more metalcarbonates, with a source of carbonate ions.

According to various embodiments, the method can comprise filteringmetal sulfates, metal carbonates, and metal hydroxides out of awastewater, for example, by using a filter press. After metal compoundsare removed from the wastewater, the wastewater can be recycled, forexample, by being pumped into a gas well hydrofracture. The metals thatcan be removed, according to various embodiments of the presentteachings, include barium sulfate, strontium sulfate, calcium carbonate,strontium carbonate, magnesium hydroxide, and strontium hydroxide. Themetals can be removed in the form of metal sludge cakes formed by afilter press, slurry, or the like.

According to various embodiments of the present teachings, the methodcan use, as a source of sulfate ions, a discharge stream from a coalmine or water from an abandoned coal mine. In some embodiments, a methodis provided whereby a liquid comprising abandoned coal mine water andgas well hydrofracture wastewater is disposed in a gas wellhydrofracture.

Accordingly to various embodiments, a method of treating a hydrofracturewastewater is provided comprising the following processes. Ahydrofracture wastewater can be contacted with a source of sulfate ionsto form one or more metal sulfates. The one or more metal sulfates canbe precipitated from the hydrofracture wastewater. The one or moreprecipitated metal sulfates can be removed from the hydrofracturewastewater to form a wastewater brine that is substantially free ofprecipitated metal sulfate. The wastewater brine can comprise sodiumchloride and calcium chloride. The wastewater brine can be evaporated inan evaporator to form water and an evaporation product. The evaporationproduct can comprise crystalline sodium chloride and a liquor comprisingfrom about 25% by weight to about 60% by weight calcium chloride basedon the total weight of the liquor. The evaporation product can befiltered to form a retentate comprising crystalline sodium chloride, anda filtrate comprising the liquor. The retentate can be washed withsaturated sodium chloride brine. The washed retentate can be dried. Insome embodiments, bromine and/or lithium can are recovered from theliquor. Various metal sulfates, such as barium sulfate, can be removedfrom the wastewater during the production of the wastewater brine. Thesource of wastewater to be treated can include, for example, gas wellproduction wastewater from a hydrofracturing process. The presentteachings relate to a process, system, equipment, and chemical reactionsfor treatment, and co-treatment with AMD, of gas well wastewaters fromcompletion, hydrofracture, and production. According to variousembodiments, the majority of gas well wastewater to be treated isproduction wastewater. This wastewater is produced during gas productionafter the gas production well is hydrofractured. The hydrofractureprocess occurs when water is mixed with fine sand and various additivesto reduce its viscosity and injected into underground gas producingformations to crack them. Hydrofracture water is removed from theformation following the fracture process to permit gas production andrecovery.

Hydrofracture or cracking of the gas bearing formation is employed toallow gas to escape to the drilled well. The sand remains in theformation to keep the cracks produced by the high pressure water openafter the pressure is released and the flowback water removed. Theremoved water, often 1.0 million to 3.0 million gallons per well, is thehydrofracture flowback wastewater, which can be either treated andreused, or sent to disposal. Production water is co-produced with gaswhen the well is in operation, with amounts generated that vary from 10gallons per day (gpd) to 4,000 gpd for the life of the well. Productionwater is generally saturated as to its ability to dissolve additionalmaterial and thus varies less than hydrofracture flowback water withregard to dissolved solids content. While both hydrofracture flowbackand production water show variation in chemical composition, the methodsof the present teachings can treat them both and the term productionwastewater can include hydrofracture flowback water and/or productionwastewaters.

With reference to FIGS. 1A and 1B, according to various embodiments ofthe present teachings, gas well hydrofracture wastewater can bedelivered for treatment to a fixed or mobile treatment process unit 100.Delivery can be by tank truck, railcar, directly from a gas well, orpumping from a wastewater containment area, for example, near a gasproduction well. The wastewater can be accumulated in an equalizationtank 102 that is of sufficient volume to retain a volume equal to atleast 8 hours of operation at the designed wastewater throughput of thetreatment process. This tank can be equipped with an aeration system 104to maintain aerobic conditions in the contained wastewater at all times.

The wastewater can be transferred from equalization tank 102 at a fixedflow rate by a pump 106, flow measurement device 108, and/or flowcontrol device, to a first process tank 110. Positive displacement pumpssuch as a progressive cavity pump equipped with a variable frequencydrive can be used. Exemplary flow rates are from 5 to 2000 gallons perminute (gpm), for example, from 10 to 1500, from 100 to 1000, or from 20to 500 gpm. Abandoned coal mine drainage (AMD) can be added to the fixedflow of wastewater at ratios of from 1:1 to 1:10, or from 1:3 to 1:4,for co-treatment. Use of AMD can reduce or eliminate the amount ofsulfate ion to be added to the first process tank for barium sulfateprecipitation. First process tank 110 can provide, for example, 5minutes of retention time at the determined fixed flow rate and can havea high rate of mixing, for example, defined as a power input of at least10 horsepower (hp) per 1000 gallons capacity. The mixer can be a highspeed mixer, for example, having an rpm of greater than 400 rpm.Furthermore, first process tank 110 can be designed to dimensions suchthat it can have a “square” cross-section when viewed.

Chemicals that can be added to first process tank 110 can includepotassium permanganate, sulfuric acid, and sodium hydroxide. Chemicaladditions can be in amounts sufficient to maintain the wastewater in anoxidized condition and within the pH range of from 3.0 to 3.5.Sufficient sulfate ion can be added to precipitate at least 50%, atleast 75%, at least 90%, at least 95%, or all of the barium in thewastewater, as barium sulfate. Wastewater from first process tank 110can be made to flow by gravity to a first process equation tank 114 andprovide approximately 50 minutes retention time at a desired flow rate.

From first process equalization tank 114, the pH-adjusted wastewater canbe pumped to a first chalked and gasketed plate and frame filter press116 at flow rates from twice to less than 10% of the design flow rate.In the pump line from tank 114 to filter press 116, a diluted, forexample, to 0.2% to 0.5% by weight, anionic polymer such as PCT 8712available from ProChemTech International, Inc., Brockway, Pa., can beadded from a supply tank 118 to flocculate the precipitates produced inthe previous two process steps. Filter press 116 can remove theprecipitates, including barium sulfate and other materials, for example,iron and manganese. Removal can be in the form of a solid sludge cakecomprising from 25% to 65% solids, for example, 40% solids. The clearliquid filtrate can be discharged from filter press 116 into a secondprocess equalization tank 120 to provide approximately 60 minutes ofretention time.

The filtrate in second process equalization tank 120 can be pumped to athird mix tank 122 to provide a retention time of 5 minutes at a desiredflow rate. Sodium carbonate can be automatically added to third mix tank122 as a dry powder to raise the pH of the wastewater to within a rangeof from 9.5 to 10.5. Under these reaction conditions, calciumprecipitates as calcium carbonate and a substantial portion of anystrontium present precipitates as strontium carbonate. The treatedwastewater can then be pH-adjusted in a fourth mix tank 124, forexample, by adding sodium hydroxide from a source tank 126. ThepH-adjusted wastewater can then be made to flow by gravity into anaerated third equalization tank 128 to provide approximately 60 minutesof retention time.

From third process equalization tank 128, the pH-adjusted wastewater canbe pumped to a second chalked and gasketed plate and frame filter press130 at a flow rate of from twice to less than 10% of the desired flowrate. In the pump line from tank 128 to filter press 130, a dilutedanionic polymer such as PCT 8712, for example, diluted to from 0.2% to0.5% by weight, can be added to flocculate the precipitates produced inthe previous process step. Filter press 130 can remove the precipitates,including mixed calcium and strontium carbonate, as a solid sludge cakecomprising from 25% to 65% solids, for example, about 40% solids. Clearliquid discharged from filter press 130 can be directed into an aeratedfourth process equalization tank 132 to provide approximately 60 minutesof retention time.

The clear, filtered wastewater from fourth process equalization tank 132can be pumped to fourth mix tank 124 to provide a retention time of 5minutes at the desired flow rate of the system. Sodium hydroxidesolution, for example, at 50% by weight, can be automatically added tofourth mix tank 124 to raise the pH of the wastewater to within a rangeof from 11.5 to 13.5. Under these reaction conditions, magnesium can beprecipitated as magnesium hydroxide and any remaining strontium can beprecipitated as strontium hydroxide. The pH-adjusted wastewater can thenbe made to flow by gravity into aerated fourth equalization tank 132, orinto a fifth equalization tank (not shown), to provide approximately 60minutes of retention time.

From third process equalization tank 128 or an optional fifth processtank (not shown), the pH-adjusted wastewater can be pumped to filterpress 130 or to a third chalked and gasketed plate and frame filterpress 134, for example, at a flow rate of from twice to less than 10% ofthe desired flow rate. In the pump line from the third or fifth processequalization tank to the filter press 130 or 134, a diluted anionicpolymer such as PCT 8712, for example, to 0.2% to 0.5% by weight, can beadded to flocculate the precipitates produced in the previous processstep. Filter press 134 can remove the precipitates, including mixedmagnesium and strontium hydroxides, as a solid sludge cake comprisingfrom 25% to 65% solids, for example, 40% solids. Clear liquid dischargedfrom the filter press can be directed into fourth equalization tank 132to provide approximately 10 minutes of retention time.

In fourth equalization tank 132, carbon dioxide gas can be automaticallyadded, for example, via diffusers, to the clear, treated wastewater toreduce the pH to within the range of from 6.5 to 8.5, for example, a pHwithin the range of from 6.5 to 7.5. The pH-adjusted, clarifiedwastewater can then be discharged by gravity into a clear water storagetank 136 for use or to be stored until subject to evaporation. If used,the pH-adjusted clarified wastewater can be used as a hydrofracturemakedown water.

According to various embodiments, if the co-treatment of AMD is usedand/or the hydrofracture wastewater has low levels of barium, calcium,magnesium, and strontium, the process filter presses can be replaced byinclined plate clarifiers. In some embodiments, inclined plateclarifiers can be used if the suspended solids level of the treatedwastewaters exiting the first, second, or third process equalizationtanks is less than 0.5% by weight. In such cases, the processequalization tanks can be eliminated from the process as processclarifiers would flow by gravity. A sludge holding tank can be providedfor each process clarifier to retain the sludge removed on an automaticbasis, for example, using positive displacement pumps. In someembodiments, three separate dewatering filter presses can be provided,one for each sludge stream. The dewatering filter presses can be fed bypositive displacement pumps from the sludge holding tanks. Filteredwaters can be returned, for example, to the system equalization tankand/or used as recycle hydrofracture water. Evaporation can beaccomplished by utilizing one or more evaporation units 138 as shown anddescribed in U.S. patent application Ser. No. 12/620,019, which isincorporated herein in its entirety by reference.

In yet another embodiment of the present teachings, a method of treatinga production wastewater is provided that can comprise the followingprocess, as described with reference to FIGS. 2A-2D. FIGS. 2A-2Dconstitute a schematic flow diagram of an exemplary wastewater treatmentsystem according to various embodiments of the present teachings,wherein flow lines A-C shown in FIG. 2C are continuations of flow linesA-C, respectively, shown in FIG. 2A, flow lines S-W shown in FIG. 2B arecontinuations of flow lines S-W, respectively, shown in FIG. 2A, flowlines D-J shown in FIG. 2D are continuations of flow lines D-J,respectively, shown in FIG. 2B, and flow lines X-Z shown in FIG. 2D arecontinuations of flow lines X-Z, respectively, shown in FIG. 2C.

In the embodiment shown in FIGS. 2A-2D a production wastewater can becontacted with a source of sulfate ions to form one or more metalsulfates. The one or more metal sulfates can be precipitated from theproduction wastewater. The one or more precipitated metal sulfates canbe removed from the production wastewater to form wastewater brine thatis substantially free of precipitated metal sulfate. The wastewaterbrine can comprise sodium chloride, magnesium chloride, strontiumchloride, and calcium chloride.

The present teachings provide a system and method to carry out chemicalreactions under various conditions for the treatment of gas wellproduction wastewater and hydrofracture wastewater. The reactions aretailored for resource recovery so as to eliminate problems otherwisepresented by disposal of such wastewaters and solid wastes generated bytreatment processes required prior to disposal. FIGS. 2A-2D show aconcept flow diagram providing a simplified process flow schematic 200.Quantities and other values for the various parameters indicated inschematic 200 are exemplary and non-limiting.

According to various embodiments, the process can begin with coalescerseparation of large solids and tramp oil from the production wastewater.The production wastewater is then equalized and aerated in storage tanksto obtain an aerobic, uniform stream for continuous treatment at flowsfrom about 0.1 gallon per minute (gpm) to about 10,000 gpm, for example,from about 1.0 gpm to about 1,000 gpm, from about 5.0 gpm to about 500gpm, or of more than about 10,000 gpm. The process can be operated as afixed site installation and/or can be trailer mounted for mobile use.Gas well production wastewater and/or hydrofracture wastewater can bedelivered for treatment at a fixed or mobile treatment process unit bytank truck, railcar, directly from a gas well, or pumped from awastewater containment area near the gas production well. Wastewater canbe accumulated in “equalization tanks”, which can have a volumesufficient to retain a volume equal to an amount generated after atleast 24 hours of operation or after another suitable time based on thedesign wastewater throughput of the treatment process. The productionwastewater can be accumulated in such an equalization tank prior tocontact with a source of sulfate ions.

Any suitable tank can be equipped with an aeration system to maintainaerobic conditions in the contained wastewater at all times, ortemporarily. In some systems, two equal volume tanks can be provided topermit continuous operation of the treatment process. This approachprovides for chemical equalization of the wastewater and can reduceoperational analysis to just once every 24 hours or at some otherdesired frequency. The treatment process can draw from a full orpartially full tank while one or more other tanks is filling. The tankscan rotate once a day, or at some other desired frequency, or as afunction of an on-line status. Equalized wastewater in the full tank canbe analyzed for barium, strontium, and/or other metal ion content priorto being pumped at a constant design flow rate from the aeratedequalization tank to the first process tank. Barium, strontium, and/orother metal ion content can determine the amount of sulfate ion added inthe first process tank.

As shown in FIGS. 2A-2D, the hydrofracture wastewater can be transferredto a first process (mixing) tank 224 after being aerated. Wastewater canbe transferred from the equalization tank to the first process tank at afixed flow rate by using a pump, a flow measurement device, and a flowcontrol device. Such methods and means can also be used for transferbetween other tanks described herein. Both positive displacement pumps,such as a progressive cavity pump, and centrifugal pumps equipped with avariable frequency drive can be employed. Typical flow rates can be fromabout 0.1 gpm to about 10,000 gpm, from about 1.0 gpm to about 5,000gpm, from about 5.0 gpm to about 2,000 gpm, or at more than about 10,000gpm. The production wastewater can be mixed in the first process tankwith a mixer 228 spinning at a rate of from about 100 rpm to about 1,000rpm, from about 250 rpm to about 750 rpm, from about 400 rpm to about600 rpm, or at a rate of greater than 1,000 rpm. First process tank 224can provide a detention time of from about 10 seconds to about 10 hours,from about 30 seconds to about 5.0 hours, from about 1.0 minute to about2.5 hours, from about 5.0 minutes to about 1.0 hour, or from about 15minutes to about 45 minutes, at a fixed, or variable flow rate. Firstprocess tank 224 can be mixed at a high rate of mixing defined as apower input of 10 horsepower (hp) per 1000 gallons capacity, or greater.Furthermore, first process tank 224 can be designed with dimensions suchthat the tank is “square” when viewed. Other tank geometries can also beemployed.

Controlled additions of an oxidant, pH adjusters, and precipitants canbe made to the wastewater in first process tank 224. Chemical additionsto first process tank 224 can include, for example, potassiumpermanganate, hydrogen peroxide, and/or sulfuric acid. A sulfuric acidsupply 232 and a hydrogen peroxide supply 236 can be provided in fluidcommunication with first process tank 224, as can a potassiumpermanganate supply (not shown). A potassium permanganate solution, forexample, 5% by weight solution based on the total weight of thesolution, or a 34% by weight hydrogen peroxide solution based on thetotal weight of the solution, can be added as an oxidizer to destroy allreadily oxidizable constituents. Sulfate ion supplied, for example, as a98% by weight sulfuric acid solution, can be added to first process tank224 in proportion to the amount of barium, strontium, or other metalions in the wastewater. The pH of the hydrofracture wastewater can beadjusted to be less than about 1.0. Chemical additions can be sufficientto maintain the wastewater in an oxidized condition and at a pH of below1.0, or at some other desired pH.

To recover salable commodities from the production wastewater whilegenerating little or no hazardous residues or non-compliant waterdischarges, the production wastewater can be first treated for removalof barium and other toxic and/or trace radioactive metals. Thehydrofracture wastewater can then be contacted with the source ofsulfate ions to form one or more metal sulfates. Sufficient sulfate ioncan be added to precipitate the desired amounts of barium, strontium,and/or other metal compounds from the wastewater as barium sulfate,strontium sulfate, and/or as other metal sulfates. Depending upon thedesired barium and/or other metal compound removal, the amount ofsulfate ion added in first process tank 224 can be adjusted fromsub-stoichiometric amounts up amounts that are 80% over a stoichiometricequivalent amount. The stoichiometry or excess stoichiometry can becalculated based on the combined amount of barium, strontium, and/orother metals present in the wastewater. For complete removal of bariumand strontium, sulfate ion can be added in an amount of 50% over, 60%over, 70% over, or 80% over the stoichiometric amount of the metals, toform barium and strontium sulfate. For the removal of less barium,proportionally less sulfate ion can be used. With the addition ofsulfate ion to the wastewater under oxidizing conditions, the bariumpreferentially precipitates.

After the contact with the source of the sulfate ions, the productionwastewater can be transferred from first process tank 224 to a secondprocess tank 240. Wastewater from first process tank 224 can flow bygravity, or be otherwise transferred, to second process tank 240. The pHof the production wastewater in second process tank 240 can be adjustedto be within a range of from about 3.0 to about 7.0, for example, fromabout 3.0 to about 5.5 or from about 3.0 to about 4.0. A sodiumhydroxide supply or other alkaline supply 244 can be provided in fluidcommunication with second process tank 240. Sodium hydroxide solution ofsuitable concentration can be added to this mix tank to obtain andmaintain a pH level between 3.0 and 4.0. In a second process step, theproduction wastewater can be strongly mixed in second process tank 240for a detention time of 5.0 minutes at the design flow rate of thesystem. Other desired mixing and detention times can be used such asthose described for the accumulation tank or for first process tank 224.Strontium, lead, radium, uranium, and/or other metal ions canprecipitate as sulfate with the higher pH maintained in the secondprocess step. Higher pH conditions, however, can cause the undesirableprecipitation of calcium sulfate.

In some embodiments, sodium hydroxide solution or another suitablealkaline solution, for example, containing about 50% by weight alkalinecomponent based on the total weight of the solution, can be added toraise the pH of the wastewater to be between about 3.0 and 4.0. ThepH-adjusted wastewater can then be transferred into a third process tank248, for example, by gravity flow. An anionic polymer can be added tothe hydrofracture wastewater in third process tank 248 to flocculatesolids. Wastewater can be mixed and/or retained in third process tank248 for a 10-minute detention time, or for a detention time as describedfor the accumulation tank, for first process tank 224, or for secondprocess tank 240, for example, at a determined fixed flow rate. Mixingin third process tank 248 can occur a high rate of mixing defined as apower input of 10 hp per 1000 gallons capacity or more. The mixer can beof a type described as low speed, for example, operating at less thanabout 400 rpm. For example, third process tank 248 can be equipped witha slow speed, VFD drive mixer. Mixers of greater speed can bealternatively employed. Furthermore, third process tank 248 can bedesigned to dimensions such that it is “square” when viewed, or it canhave another desired geometry.

The anionic polymer can comprise any suitable anionic polymer, forexample, PCT 8727, available from ProChemTech International, Inc.,Brockway, Pa. The anionic polymer can be pre-diluted. The anionicpolymer can be added to third process tank 248 to flocculate theprecipitated particles resulting from the previous two process steps.For example, a solution of PCT 8727 can be added to third process tank248 from an anionic polymer supply 252 to obtain a concentration of from2.9 to 10.0 mg/l as active product in third process tank 248. PCT 8727can be supplied, for example, as a 0.2% by weight to 0.5% by weightaqueous solution based on the total weight of the aqueous solution.

The wastewater can be discharged from third process tank 248 into aninclined plate clarifier 256, or analogous device, by flowing bygravity, or other means, preferably with little or no head loss. Theprecipitated and flocculated solids can then be removed as a sludge fromthe bottom of the clarifier by a positive displacement pump 260 andtransferred to a sludge thickening tank 264. Sludge can be pumped to anappropriate dewatering and washing device such as a horizontal beltpress, a filter press, or a rotary vacuum drum filter. The sludge can befirst dewatered with filtrate that is then returned to the brine storagetank, and then the sludge can be washed with water that has lowdissolved solids, for example, less than 500 mg/l solids. Spent washwater can be returned to an off-line equalization tank, evaporator, orwastewater brine storage tank. The dewatered sludge can then be washedto form a washed sludge. The dewatered and washed sludge can then bedried and placed into a storage pile 280 as a commodity consistingmainly of barium sulfate or barite.

As described above, the production wastewater can be clarified to formwastewater brine and sludge. The sludge can comprise the precipitatedmetal sulfates and flocculated solids. The wastewater brine can comprisea sodium chloride brine 284 from washing the sludge. The used brine canbe collected and the collected brine can be introduced into anevaporator 288. Sludge cake produced is non-hazardous and is suitable,with optional further processing, for use as a drilling mud additive,for use as a component of glass batch, or for other uses well known for“barite.”

The clarified wastewater, which is now a brine, can be discharged bygravity into a clear well 268 and can be pumped to a brine storage tank272. Brine produced by the foregoing process is acceptable for use ashydrofracture makeup water and can be collected for use, for example,from brine storage tank 272. The wastewater brine can have a pH of fromabout 1.0 to about 14.0, from about 1.5 to about 12.0, from about 2.0 toabout 8.0, or from about 3.0 to about 4.0. The brine can be sold as acommodity, for example, as hydrofracture makeup water, and can besupplied from brine storage tank 272, or from a hydrofrac brinereservoir 274.

According to various embodiments of the present teachings, whenproduction wastewater from which barium and other toxic metals have beenremoved, is concentrated by evaporation, the sodium chloride therein canfractionally crystallize from the solution, leaving a liquor thatincludes mainly calcium chloride in solution. Typically, concentratingthe brine to a calcium level of 180,000 mg/l will cause an initialsodium level of 80,000 mg/l to decrease to a level of less than 2,000mg/l. The calcium concentration factor with typical productionwastewater is approximately 10 times its original concentration, but anydesired concentration can be employed, for example from about 1 time toabout 100 times, from about 2 times to about 75 times, from about 3times to about 60 times, from about 5 times to about 25 times, orgreater than about 100 times the original concentration. The wastewaterbrine can be evaporated in evaporator 288 to form water and anevaporation product. The evaporation product can comprise crystallinesodium chloride and a liquor comprising from about 25% by weight toabout 60% by weight calcium chloride based on the total weight of theliquor. Brine can be pumped to an appropriate evaporator andconcentrated by evaporation to reach a calcium chloride concentration inthe concentrate or liquor, of from about 10% by weight to about 80% byweight based on the total weight of the solution, for example, fromabout 25% by weight to about 60% by weight, or from about 40% to about50% by weight. The amount of concentration can be governed by the amountof residual sodium desired in the liquor following dewatering to removecrystallized sodium chloride. Concentration to higher levels of calciumchloride result in lower levels of sodium chloride in the final calciumchloride solution.

According to various embodiments of the present teachings brine producedby that first precipitation process can be concentrated by evaporation,which results in a fractional crystallization of sodium chloride thatcan then be recovered as a salable commodity. Due to differingsolubilities, sodium chloride fractionally crystallizes from the liquor,with low levels remaining in solution, at appropriate concentrations ofcalcium. In some embodiments, the appropriate level of calcium expressedas calcium chloride is in the range of from about 25% by weight to about60% by weight based on the total weight of the solution. This level canbe adjusted depending upon the desired level of sodium in the liquorfiltrate. Increasing the level of calcium chloride substantially reducesthe amount of sodium dissolved in the liquor. For example, at a level of32% by weight calcium chloride, the sodium level is 24,500 mg/l, whereasat a level 53% calcium chloride, the sodium level drops to just 3,350mg/l. These amounts are based on starting brine having a sodium level of80,000 mg/l. The wastewater brine can be mixed in the evaporator at anydesired rate using any desired mixing apparatus or method. For example,the wastewater brine can be mixed in the evaporator during theevaporating by using a mixer spinning at a rate of greater than about400 rpm.

To produce a desirable crystalline sodium chloride, the liquor in theevaporator can be subject to high speed mixing the entire time it iswithin the evaporator, or for a substantial portion of the time. Highspeed mixing can be provided as described for the various accumulationand process tanks. The evaporator can comprise a steam-heated kettle, amultiple effect vacuum unit, a vapor recompression apparatus, or acombination thereof. If a multiple effect vacuum unit is used, it cancomprise one, two, three, or more stages, and can incorporate vaporrecompression and a cooling stage prior to dewatering of the liquor. Theevaporator can incorporate a cooling stage to increase the amount ofsodium chloride. The evaporation product can be cooled prior to thefiltering, during filtering, and/or after filtering.

The system can further comprise a heat recovery device that can producedistilled water as yet another product. The water formed from theevaporating can be collected. As most evaporators utilize heat recoveryfrom produced water vapor, which results in condensation of water, thetreatment process can produce a side stream of distilled water. Thisdistilled water can be collected in a storage tank 296 and used inprocess reagent preparation, used as wash water, or sold as a commodity.In the event that excess distilled water is produced, it can bedischarged to a POTW or to surface waters under an appropriate permit.Water vapor from the evaporator can be passed through a condenser forenergy recovery, which also results in production of distilled water.For discharge to surface waters, the distilled water must meet the PADEPeffluent limitation on dissolved solids. In some cases, the distilledwater can be used in such applications as boiler and cooling towermakeup water, chemical manufacture, or various process applications. Insome embodiments of the process, a portion of the distilled water can beutilized within the process for makeup of the various solutions involvedin barium removal and to prepare saturated sodium chloride brine forrinsing of the crystalline sodium chloride.

From the evaporator, the brine containing crystallized sodium chloride(slurry) is transferred, for example, pumped, to an appropriatedewatering and washing device 300. Filtering, dewatering, and relatedprocesses can be carried out using any suitable means or method. Forexample, dewatering can be performed with a device that comprises achalked and gasketed plate, a frame filter press, a horizontal bedpress, a rotary drum vacuum filter, or a combination thereof. A slurryholding tank can be provided depending upon the dewatering deviceselected. Liquids from the dewatering and washing steps can be returnedto an off-line equalization tank. Liquor can be removed from theevaporator on a continuous basis to an appropriate dewatering andwashing device such as a horizontal belt press, a filter press, or arotary vacuum drum filter. The crystalline sodium chloride is firstdewatered and then washed with saturated sodium chloride brine forremoval of calcium. The evaporation product can be filtered to form aretentate comprising crystalline sodium chloride, and a filtratecomprising the liquor.

The retentate can be washed with saturated sodium chloride brine. Thewashed retentate can be dried. The crystalline sodium chloride can thenbe removed from the liquor by filtration and purified by rinsing withsaturated sodium chloride brine to remove as much calcium and magnesiumchloride from the product as possible. The crystalline sodium chloridecan be dewatered, washed, and dried. The crystalline sodium chloride canbe sold into commerce as salt for chemical production, roadway deicing,or water softening, among other uses. Saturated sodium chloride brinerinse can be used to prevent dissolution of the crystalline sodiumchloride while providing good removal of calcium and magnesium chloridefrom the product. Spent wash water, preferentially consisting ofsaturated sodium chloride brine, can be returned to the evaporator. Thespent saturated sodium chloride brine from rinsing of the crystallinesodium chloride can also be returned to the evaporator for recovery ofboth sodium chloride and calcium chloride values. Dried crystallinesodium chloride can be discharged to a storage silo 304 and sold as acommodity. Spent wash water can be returned to the evaporator.

The liquor and filtrate remaining after removal of the crystallinesodium chloride can also be a salable commodity, in the form of acalcium chloride solution. The filtrate from dewatering the crystallinesodium chloride can be tested for specific gravity by an on-lineinstrument, or by other means, and if within a certain specification canbe pumped to a calcium chloride solution storage tank 308. Calciumchloride of a set specification can be a salable commodity. If in anacceptable range of specific density, for example, from 1.2 to 1.5, itcan be transferred to storage tanks for subsequent sale into commerce asliquid calcium chloride solution for use as a dust control agent, freezeproofing of bulk minerals, or concrete additive, or used for chemicalproduction processes among other uses. Liquor not meeting thespecification can be returned to the evaporator for further removal ofwater.

If bromine and lithium are present in the liquor and filtrate, recoveryof bromine and lithium values can also be included in the process,depending upon the economic value of the recovered materials. If theliquor and filtrate contain economically recoverable amounts of bromineand lithium, the liquor and/or filtrate can be processed for recovery ofthese materials as commodities. Bromine can be recovered from at leastone of the liquor and the filtrate. Bromide can be recovered byelectrolysis of the brine under vacuum. Bromine gas can be dischargedand recovered as sodium hypobromite via an alkaline gas scrubber.Bromine recovery can comprise electrolyzing at least one of the liquorand the filtrate to form bromine gas, using a vacuum to remove thebromine gas, and scrubbing the bromine gas into a sodium hydroxide orother alkaline solution to produce a sodium hypobromite solution.Recovery of bromine from the liquor by known electrolysis methods can beincorporated independent of, or depending upon, the economics of therecovery and the commodity price of bromine.

Recovery of lithium from the liquor by known ion exchange andnanofiltration methods can be incorporated independent of or dependingupon the economics of the recovery and the commodity price of lithium.Lithium can be recovered from at least one of the liquor and thefiltrate. Lithium recovery can comprise subjecting at least one of theliquor and the filtrate to selective ion exchange, to concentration bynanofiltration, or to both. Lithium recovery can comprise contacting atleast one of the liquor and the filtrate with a source of carbonate ionsunder conditions to form lithium carbonate, and subsequentlyprecipitating the lithium carbonate.

With reference to FIGS. 2A-2D, in an exemplary treatment for resourcerecovery of a Marcellus production wastewater, the process can begin byreceiving production wastewater by tank truck or rail tank car delivery.As the production wastewater is unloaded, it can pass, by gravity flow,through a media coalescer for removal of tramp free oil and larger,greater than 35 microns, suspended solids. The coalescer filteredproduction wastewater can then be pumped into one of two 24-hourcapacity aerated equalization tanks. The equalization tanks can berotated in service so that each tank can provide for 24 hours ofoperation of the following treatment process so as to minimize chemicalanalysis of the production wastewater and subsequent treatment processset-up.

The full equalization tank can be sampled and analyzed for barium andstrontium concentration for use in process set-up. Sulfate ion additioncan be calculated in terms of 98% sulfuric acid at 1.7 times thestoichiometric amount needed to react with the barium and strontiumamount present in the production wastewater to be treated as determinedby analysis. Equalized and aerated production wastewater can be pumpedfrom one of the provided equalization tanks at a typical rate of 500,000gpd, through a flow meter, to mix tank #1.

In mix tank #1 five minutes of retention time can be provided with highenergy mixing, and the determined amount of sulfuric acid can be meteredinto the mix tank via a chemical metering pump from a bulk sulfuric acidstorage tank. The chemical metering pump can be set to deliver theamount of sulfuric acid determined to provide the desired amount ofsulfate ion. Hydrogen peroxide, 34% by weight, can also be metered intomix tank #1 via a pump and valve delivery system from a bulk storagetank to obtain a level of 600 mg/l.

Production wastewater can then flow by gravity to mix tank #2 where fiveminutes of detention time can be provided with high energy mixing. Anautomatic pH control system can control metered addition of 50% sodiumhydroxide solution via a pump and valve delivery system from a bulkstorage tank to maintain a pH of between 3.5 and 4.0 in mix tank #2.

Production wastewater can then flow by gravity to mix tank #3 where tenminutes of detention time can be provided with medium energy mixingsupplied via a VDF equipped mixer. An amount of made down polymer, PCT8727 polymer, 0.2% by weight in water, can be metered into mix tank #3via a pump and valve delivery system from a bulk makedown unit to obtain3 mg/l polymer in the wastewater. The PCT 8727, or another flocculant,can be used to flocculate the barium precipitate formed by chemicalreactions in mix tanks #1 and #2.

Flocculated wastewater can then be made to proceed by zero head lossgravity flow from mix tank #3 to an inclined plate clarifier configuredto provide 0.25 gpm flow per square foot of projected plate area. For500,000 gpd, the clarifier can have a minimum projected plate area of1,389 sq ft. and a minimum actual plate area at 60 degrees of 2,778 sqft.

Flocculated barium sludge can drop to the bottom of the inclined plateclarifier and be removed to a sludge thickener by a positivedisplacement pump configured to maintain a minimum depth of sludge inthe clarifier sludge hopper.

Barium sludge can be transferred from the sludge thickener to ahorizontal belt filter (HBF) where in a first vacuum stage brinewastewater is removed from the sludge. Recovered brine wastewater canthen be pump transferred to the brine water storage tank.

The second stage of the HBF can provide a distilled water rinse of thesludge, which can be in the form of a solid cake of barite, to removeremaining soluble salts. The spent wash water can be is pumped to amulti-effect evaporator for recovery of both the soluble salts and thedistilled water.

Barite cake can be discharged from the HBF and conveyed to a rotarydryer to reduce its moisture content to below 1%. The dried barite canthen be conveyed to a roofed storage pile prior to shipment off-site.

Clarified brine wastewater can be discharged from the inclined plateclarifier into a clear well tank from which it can be pumped to a brinewastewater storage tank. Clarified brine wastewater can, at this point,be sold off-site for use as hydrofracture makeup water.

Clarified brine wastewater can be transferred by pump to a steam heated,mechanically mixed multi-effect evaporator where water can be removed byevaporation. Evaporators as described in U.S. patent application Ser.No. 12/620,019 can also or instead be used. When sufficient water hasbeen evaporated, the sodium chloride content of the brine wastewater canprecipitate from solution. A control point for the multi-effectevaporator can be to obtain a 40% by weight concentration of calciumchloride in the evaporator liquor which minimizes the sodium chlorideremaining in solution to less than 3% by weight. A salt slurry,consisting of evaporator liquor and precipitated sodium chloridecrystals, can be drawn from the evaporator on a continuous basis andtransferred to another HBF where, in a first vacuum stage, liquor can beremoved and pumped either back to the multi-effect evaporator or to acalcium chloride solution storage tank dependent upon its specificgravity. Specific gravity can be measured by an on-line instrument witha typical setting of 1.4 for discharge to the storage tank.

In the second stage of the HBF, sodium chloride brine can be utilized towash the precipitated sodium chloride crystals to remove soluble calciumsalts, magnesium salts, and strontium salts from the product. Spent washcan be pumped back to the multi-effect evaporator for recovery of saltsand distilled water.

The third stage of the HFB can be utilized to dry the sodium chloridecrystals via hot air passage through the product. Dry product can thenbe discharged from the HBF and conveyed to a storage silo prior tooff-site shipment.

Water vapor can be discharged from the multi-effect evaporator andcondensed into distilled water that can be stored in a distilled waterstorage tank. Distilled water is a commodity that can be sold or aproduct that can be utilized in the process for cooling tower makeup,boiler makeup, barite rinse water, and/or polymer makedown. Any excesscan be discharged to an available sanitary sewer or to stream withappropriate permits.

The process can be supported by typical plant utilities in the form of a3400 ton capacity cooling tower system providing cooling for themulti-effect evaporator and a 2000 hp boiler providing steam to themulti-effect evaporator. In some cases, a boiler can be used to supplysteam for a fractional crystallizer, to heat air used to dry sodiumchloride, barite, and other products in processes where the product isdried, or a combination thereof. In cases where a fluidized bed dryer isused to dry a product, such as sodium chloride, the source of heat forthe fluidized bed dryer can be steam from a boiler.

The present teachings also relate to the system shown in FIGS. 2A-2D,which can be used to carry out the methods described herein. In someembodiments the system can comprise all of the components shown in FIGS.2A-2D and in other embodiments a subsystem can be provided thatcomprises just the components encompassed within the dashed lines shownin FIGS. 2A-2D. In some embodiments the components not encompassedwithin the dashed lines can be supplied separately or can bepre-existing at a site where the method is to be carried out.

FIGS. 3A-3C are collectively a process flow diagram showing an exemplaryprocessing method and system according to yet another embodiment of thepresent invention. The partial flow diagram shown in FIG. 3A connects tothe partial flow diagram shown in FIG. 3B along flow lines X and Y. Thepartial flow diagram shown in FIG. 3A connects to the partial flowdiagram shown in FIG. 3C along flow line Z. The partial flow diagramshown in FIG. 3B connects to the partial flow diagram shown in FIG. 3Calong flow lines A-E. The flow diagram shown in FIGS. 3A-3C depicts boththe system components and method components of the present invention.The process begins at unloading docks 320 where wastewater can bedelivered to the system, for example, by tanker trucks. The unloadingdocks shown are exemplified as comprising docks for six tanker trucks.The unloading dock can be diked. Wastewater unloaded from the tankers atthe unloading docks can be moved to a dual separator 324 that caninitially separate solids and tramp oil from the wastewater. Separatedsolids can be moved to a solids receptacle or vessel 328, and separatedtramp oil can be moved to a receptacle or vessel 330. The treatedwastewater is then moved from dual separator 324 to one or more aeratedstorage equalization tanks.

In the exemplary embodiment shown in FIGS. 3A-3C, two aerated storageequalization tanks are used, 332 and 334. Each tank 332 and 334 canindependently hold 10,000 gallons or more, for example, 50,000 gallonsor more, 100,000 gallons or more, or, as exemplified, 300,000 gallons.After an appropriate aeration treatment, the treated wastewater or aportion thereof can be moved from tanks 332 and 334 to a first mix tank336 where the wastewater can be mixed with an acid and an oxidizingagent. In the embodiment exemplified, the wastewater is mixed in mixtank 336 with a solution of 98% by weight sulfuric acid pumped into mixtank 336 from a vessel 338. A separately supplied source of potassiumpermanganate can be pumped or otherwise supplied from a vessel 340 intomix tank 336. Although hydrogen peroxide can be used instead ofpotassium permanganate, the use of potassium permanganate has been foundto provide superior results as an oxidizing agent. After mixing isenabled in mix tank 336, the mixed and treated wastewater can then bemoved to a second mix tank 342 where it can be mixed with an alkalinereagent, for example, as shown, a 50% solution of sodium hydroxidepumped in from a vessel 344. Although 50% sodium hydroxide isexemplified, any suitable non-toxic alkaline reagent can be used. Aftermixing with the sodium hydroxide in mix tank 342, the treated liquid canthen be moved to a third mix tank 346 wherein the liquid can be treatedwith a flocculating agent, for example, PCT 8727 (available fromProChemTech International, Inc., of Brockway, Pa.). The flocculatingagent can be pumped in from a vessel 348. After a treatment period thatis sufficient to enable flocculation in mix tank 346, the liquid is thenmoved to an inclined plate clarifier 350 to separate the slurry into aclarified brine and a barite sludge. The slurry in inclined plateclarifier 350 can be recycled back to mix tank 336, as shown. Forexample, the slurry, including precipitated barium sulfate, can berecycled from inclined plate clarifier 350 along a recycle line 351 andreturned to mix tank 336 for another round of mix tank processing.Recycling such output from inclined plate clarifier 350 has been foundto produce a superior crystalline structure in the recovered productsgenerated from the system and method. After recycling, barite sludgeexiting inclined plate clarifier 350 can be collected in barite sludgetank 352 and then subjected to further processing as described below.

Clarified liquid leaving inclined plate clarifier 350 can be received ina brine well tank 354. Brine from tank 354 can then be moved to a firstheat exchanger 356 before being passed through to an evaporatorcrystallizer 358. A pH neutralization tank (not shown) positioneddownstream of inclined plate clarifier 350 can be provided to increasethe alkalinity of the brine before it is evaporated and crystallized.For example, sodium hydroxide can be added to the brine in a pHneutralization tank to obtain a pH of from about 6.5 to about 7.5, orbetween 6.5 and 7.5, before the brine reaches evaporator crystallizer358. Adjusting the pH to be within such ranges has been determined toreduce corrosion of evaporator crystallizer 358 and related equipmentutilized for further processing of the brine.

A recirculating heating system including a boiler 360 can be provided toheat the brine received in the evaporator crystallizer 358. As shown inFIG. 3B, heat in the form of heated water from the evaporatorcrystallizer 358 can be used by heat exchanger 356 to warm incomingbrine. Water collected in evaporator crystallizer 358 can travel fromheat exchanger 356 into a second heat exchanger 357 and can exit heatexchanger 357 in the form of distilled water that can be received in adistilled (DI) water tank 364. The boiler can be used to supply steamfor the evaporator crystallizer, to heat air used to dry sodiumchloride, to heat air used to dry barite sludge, to heat air used to dryother products in processes where the product is dried, or a combinationthereof. In cases where a fluidized bed dryer is used to dry a product,such as sodium chloride, the source of heat for the fluidized bed dryercan also be steam from the boiler.

Heat exchanger 357 can be in thermal contact with a cooling tower 362.Cooling tower 362 can be replenished, as need, by a cooling tower makeupvessel 366. Water from DI water tank 364 can be pumped or otherwise fedinto cooling tower makeup vessel 366, as needed. Any of a plurality ofagents, reagents, and/or materials can be added to the stream of wateras the stream is moved to cooling tower makeup vessel 366. For example,polymer makeup from a vessel 368, boiler makeup from a vessel 370, andpotassium permanganate or another oxidizing agent from a vessel 372, caneach independently be added to the stream of water, as needed, as thestream is moved from DI water tank 364 to cooling tower makeup vessel366. Although not shown, water from water tank 364 and the variousagents, reagents, and/or materials from vessel 368, 370, and 372, can bepumped to other components or parts of the system, for example, boilermakeup from 370 can be fed to one or more boilers in the system. One ormore of the boilers in the system can be used to supply steam for theevaporator crystallizer, to heat air used to dry the sodium chloride, toheat air used to dry the barite sludge, to heat air used to dry otherproducts in processes where the product is dried, or a combinationthereof. In cases where a fluidized bed dryer is used to dry a product,such as sodium chloride, the source of heat for the fluidized bed dryercan also be steam from one or more of the boilers.

Sodium chloride can be removed from evaporator crystallizer 358 througha product line 359 and can be cooled by passing through a heat exchanger374. Cooled product leaving heat exchanger 374 can then be fed into alinear belt filter press 376. Brine from brine makeup tank 378 can bepumped to linear belt filter press 376, for example, to wash crystallinesodium chloride product that is captured by linear belt filter press376. A boiler 371 can be connected to linear belt filter press 376through a recirculating circuit and can provide heat to the press.Sodium chloride separated by liner belt filter press 376 can be rinsedwith brine makeup from vessel 378 and the rinse brine can be directed toa spent wash tank 394 before being moved to brine well tank 354. Thus,the liquid from evaporator crystallizer 358 can be dewatered from linearbelt filter press 376, and recirculated to evaporator crystallizer 358,without being diluted by the brine from vessel 378.

After dewatering in linear belt filter press 376, sodium chlorideproduct can be conveyed to and collected in a sodium chloride vessel380, and from there they can be moved to a conveyor 382. Solid sodiumchloride product can be moved along conveyor 382 to a hopper 384, andfrom hopper 384 into a bulk silo tank 386. Sodium chloride product frombulk silo tank 386 can be packaged in the form of a product 388 andhauled away by truck, rail car, or the like.

The sodium chloride product from evaporator crystallizer 358 can insteador also be recovered from the evaporation liquor by utilizing ahydrocyclone concentration of solids followed by a high speed centrifugefor solid product recovery. The centrifuge can be equipped to wash therecovered sodium chloride with saturated sodium chloride brine, forexample, as described above, if required by product specifications.Recovered sodium chloride can then be dried, for example, using afluidized bed dryer, prior to storage, packaging, and/or bulk shipment.

After removing sodium chloride crystalline product in linear belt filterpress 376, the liquid from dewatering can then be tested in a specificgravity tester 410 to determine whether the liquid has a high enoughconcentration of calcium chloride to be collected as a product. Forexample, if the specific gravity is high enough to correspond to aconcentration of 65% by weight or more, calcium chloride, then theconcentrated calcium chloride liquid can be diverted to a calciumchloride storage tank 390 and from there pumped into a dilution storagetank 392. Calcium chloride solution in dilution storage tank 392 can bediluted with DI water supplied from DI water vessel 398 to achieve anexact concentration for product packaging and labeling. The resultingcalcium chloride product 399 can then be sold. If the calcium chloridesolution dewatered from and exiting linear belt filter press 376 isdetermined by the specific gravity tester 410 to be of insufficientconcentration for final processing, the solution can then be returned toevaporator crystallizer 358 for further processing and concentrating.

For optional recovery of strontium sulfate and to produce a superior lowstrontium-content final calcium chloride product, an additional three(3) mix tanks, mix tanks 4, 5, and 6 (not shown), and an additionalinclined plate clarifier (not shown), can be added to the system after,or immediately downsteam from, inclined plate clarifier 350, forsequential recovery of strontium sulfate. Such an additional sub-systemis exemplified in FIG. 4 described below.

Referring again to FIG. 3A, barite sludge from barite sludge tank 352can be pumped along pathway Z, through the continuation of pathway Zshown in FIG. 3C, and into a filter press 396 as shown in FIG. 3C.Barite sludge dewatered from filter press 396 can be collected in avessel 400 and then moved to a dryer 402. Spent wash from dewatering infilter press 396 can be moved to spent wash vessel 394 and then movedinto brine well tank 354 to be used and processed as discussed above.After drying in dryer 402, the barite sludge can be moved to and along aconveyor 404 to a hopper 406. Dried barite sludge exiting hopper 406 canbe bagged at a bag fill station 408. It has been determined that thebarium precipitation also removes substantially all iron, manganese,radium, and suspended solids from the wastewater being treated. Theseconstituents are thus incorporated into the recovered barite sludge.

It has been discovered that the recovered barite sludge may be a salableproduct without dewatering and washing. In an alternative to therecovery process shown, recovered barite sludge can instead be furtherconcentrated in a thickener and delivered, sold, or both, as a slurry.For example, the barite sludge can be concentrated in a thickener, andthen stabilized by the addition of materials such as calcium ligninsulfonate, various polymers such as polyacrylate, combinations thereof,and the like. The stabilized product can then be pH-adjusted withvarious caustic materials such as sodium hydroxide, sodium silicate, acombination thereof, or the like. The final product can then be storedin a tank and delivered as a liquid slurry.

If it is desired to recover a strontium sulfate sludge and/or to removestrontium and provide a low strontium-content calcium chloride product,and additional sub-system can be used, as exemplified in FIG. 4. Asshown in FIG. 4, incoming treated wastewater, for example, exitinginclined plate clarifier 350 shown in FIG. 3A, can be moved or otherwisedirected to a fourth mix tank, depicted in FIG. 4 as mix tank 436.Barium from the original wastewater can be substantially removed beforeincoming to mix tank 436. For example, if the sulfuric acid addition tomix tank 336 (FIG. 3A) is adjusted to provide an amount of sulfate ionthat is equal to from about 100% to about 150% of a stoichiometricallyequivalent amount of barium contained in the wastewater being treated inmix tank 336, substantially all of the barium can be precipitated asbarium sulphate. Then, additional sulfuric acid can be added to mix tank436 (FIG. 4) in an amount of from about 100% to about 150% of astoichiometrically equivalent amount of strontium in the incomingwastewater being treated in mix tank 436. Mix tank 442 can then be usedto adjust the pH, for example, to increase the pH. Mix tank 442 can beused to adjust the pH to be within the range of from about 6.5 to about7.5, or to be between 6.5 and 7.5, by addition of sodium hydroxide oranother alkaline or pH-adjusting reagent.

Mix tank 446 can be used to mix the wastewater with an anionic polymerto flocculate solids. Strontium sulfate can then be recovered in theadditional inclined plate clarifier 450 and subsequently moved to andretained in a separate strontium sludge tank 452. The strontium sulfatesludge can then be washed, dewatered, and dried, for example, using afilter press and dryer. The dried strontium sulfate can then be baggedand sold as a bagged strontium sulfate product. Recycling of the slurryfrom inclined plate clarifier 450, containing precipitated strontiumsulfate, back into mix tank 436 can be enabled by a recycle line 451.The extent of recycling can depend upon the crystalline structuredesired in the recovered products, for example, in the subsequentlygenerated sodium chloride. In the event that recovered barite is washedas part of the recovery process exemplified in FIGS. 3A-3C, spent baritecake wash water can be directed to mix tank 436 if strontium is to berecovered, for example, using the sub-system shown in FIG. 4.

Some wastewaters have been reported to contain significant amounts ofboth free and dissolved hydrocarbons. Various techniques can be employedto remove these constituents such as dissolved air floatation, with andwithout chemical emulsion breaking, and various membrane processes.

Dependent upon the specific process train employed and wastewatercharacteristics, distilled water may be produced in excess of facilityneeds and can thus be sold as an additional salable product.

The recovery process and system of the present invention areparticularly useful in treating Marcellus deposit wastewaters, but canalso be applied to wastewaters from other gas and oil shale plays. Insome cases, the process and system can entail one or more additionalpretreatment and/or concentration steps. The following Table 4 shows thelevels of dissolved solids in wastewaters from some other shale plays.

TABLE 4 Shale play median total dissolved solids in mg/l Anadarko132,200 Denver 10,200 Permian 89,200 Williston 132,400

Wastewaters with dissolved solids levels below 200,000 mg/l can bepre-concentrated using technologies such as the low temperatureevaporation disclosed in U.S. Pat. No. 8,834,726 B2, which isincorporated herein in its entirety by reference. Other pre-treatmentmethods that can be used include higher temperature evaporation using asteam-heated kettle, a multiple effect vacuum unit, a vaporrecompression apparatus, a combination thereof, or the like. Whenwastewater dissolved solids levels are below 50,000 mg/l, a membraneprocess such as a reverse osmosis process can be used.

EXAMPLES Example 1

The wastewater treatment system and process described with reference toFIGS. 2A-2D were used on a typical Marcellus production wastewater andgenerated the results shown below in Table 5.

TABLE 5 Production Parameter Wastewater Treated Brine Produced Liquorbarium mg/l 6,000 43 50 bromide mg/l 812 1.020 9,632 calcium mg/l 17,50019,300 182,000 lithium mg/l 189 220 2,050 magnesium mg/l 1,800 1,54014,750 sodium mg/l 80,000 55,500 2,600 strontium mg/l 3,600 1,280 10,100

As noted in U.S. patent application Ser. No. 12/620,019, the recoveredbarium sulfate, barite, from the first separation is a salablecommodity. The crystalline sodium chloride obtained from the fractionalcrystallization step was recovered and compared with a commercial sodiumchloride product as shown in Table 6 below.

TABLE 6 Parameter Commercial product Crystalline product sodium chlorideminimum 97% 98%

Furthermore, the produced liquor, after filtration removal of thecrystalline sodium chloride, met the specifications received for thecommodity sale of technical calcium chloride solution.

Example 2

The wastewater treatment system and process described with reference toFIGS. 2A-2D were used on a second typical Marcellus productionwastewater and generated the results shown below in Table 7.

TABLE 7 Production Parameter Wastewater Treated Brine Produced Liquorbarium mg/l 325 not detected not detected bromide mg/l 2,660 7,030calcium mg/l 19,600 21,500 99,400 lithium mg/l 93.0 440 magnesium mg/l1,945 2,120 9,720 sodium mg/l 41,000 36,000 24,00 strontium mg/l 2,3601,920 34,000

As noted in U.S. patent application Ser. No. 12/620,019, the recoveredbarium sulfate, barite, from the first separation is a salablecommodity. Furthermore, the produced liquor, after filtration removal ofthe crystalline sodium chloride, met the specifications received for thecommodity sale of technical calcium chloride solution. Producedcrystalline sodium chloride was found to meet the specifications forsale as a commercial sodium chloride product.

Example 3

Fractional crystallization analyses and solubilities, as depicted inTable 8 below, shows how the solubility of sodium chloride decreases asthe concentrations of calcium chloride and magnesium chloride increase.

TABLE 8 Fractional Crystallization - NaCl, results as g/100 ml solution= % by weight Temperature C. CaCl₂ MgCl₂ NaCl 18 22.7 5.5 5.4 50 22.77.8 6.0 50 44.8 7.1 0.5 50 56.4 0 0.6 95 33.8 8.4 2.3 95 52.9 8.2 0.9 9560.1 0 0.98 95 60.2 0 0

Thus, by evaporation, all three salts can be concentrated, but as thecalcium and magnesium levels increase, the sodium chloride becomes lesssoluble and precipitates out of solution as a pure crystalline material.The solubility table shows that as the mixed salt solution isconcentrated both sodium chloride and magnesium chloride canfractionally crystallize out of solution. Commercial productspecifications, such as the two sets of specifications shown below,permit a substantial amount of magnesium in liquid calcium chlorideproducts.

Commercial Product Specifications #1, for Liquid Calcium ChlorideCaCl₂—28 to 40% NaCl—1.68 to 2.52% MgCl₂—0.15 to 0.23% CommercialProduct Specifications #2, for Liquid Calcium Chloride CaCl₂—28 to 40%NaCl—1.0 to 3.5% MgCl₂—0.8 to 3.4%

Thus, by minimizing only the sodium level, the process can produce apure sodium chloride that can be sold as a commodity.

Table 8 enables an optimization of product recovery. For example, fromTable 8 it can be seen that calcium chloride can be concentrated to avalue of from about 52.9% to 60.1% calcium chloride, by weight, forexample, about 55.5% by weight, to give a magnesium chloride value ofless than 3% by weight and a sodium chloride value of less than 1.0% byweight at 95° C. Table 8 also shows that the method can be operated at50° C., using heat recovery, to give an optimum calcium chlorideconcentration of 49.7% by weight or a range, for example, of from about44.8% by weight to about 56.4% by weight.

The present invention includes the following numbered aspects,embodiments, and features, in any order and/or in any combination:

-   -   1. A method of treating a gas well hydrofracture flowback and/or        production wastewater (production wastewater), comprising:        -   contacting a production wastewater comprising barium, with a            source of sulfate ions, in a first tank and under conditions            to precipitate barium sulfate;        -   precipitating barium sulfate from the production wastewater            in the first tank to form a slurry of precipitated barium            sulfate and a wastewater brine, the wastewater brine            comprising sodium, magnesium, strontium, and calcium            chlorides;        -   moving the slurry to a second tank;        -   mixing the slurry with a second reagent in the second tank;        -   recycling the slurry to the first tank and repeating the            precipitating, moving, and mixing to form a refined            wastewater brine; and        -   evaporating the refined wastewater brine to form water and            evaporation products, the evaporation products comprising            crystalline sodium chloride.    -   2. The method of any preceding or following        embodiment/feature/aspect, wherein the evaporating further        comprises forming a liquor comprising from about 25% by weight        to about 60% by weight calcium chloride based on the total        weight of the liquor.    -   3. The method of any preceding or following        embodiment/feature/aspect, further comprising filtering the        evaporation product to form a retentate comprising crystalline        sodium chloride, and a filtrate comprising the liquor;        -   washing the retentate with saturated sodium chloride brine;            and        -   drying the washed retentate.    -   4. The method of any preceding or following        embodiment/feature/aspect, further comprising cooling the        evaporation product prior to the filtering.    -   5. The method of any preceding or following        embodiment/feature/aspect, further comprising measuring the        specific gravity of the filtrate.    -   6. The method of any preceding or following        embodiment/feature/aspect, further comprising:        -   moving the refined wastewater brine to a third tank;        -   adding from about 100% to about 150% of a stoichiometrically            equivalent amount of sulfate ions to the third tank, based            on the amount of strontium ions in the third tank; and        -   precipitating strontium sulfate in the third tank.    -   7. The method of any preceding or following        embodiment/feature/aspect, further comprising recovering and        drying the precipitated strontium sulfate.    -   8. The method of any preceding or following        embodiment/feature/aspect, wherein the contacting comprises:        -   adding from about 100% to about 150% of a stoichiometrically            equivalent amount of sulfate ions to the first tank, based            on the amount of barium ions in the first tank.    -   9. The method of any preceding or following        embodiment/feature/aspect, further comprising adjusting the pH        of the refined wastewater brine to be between 6.5 and 7.5,        before the evaporating.    -   10. The method of any preceding or following        embodiment/feature/aspect, wherein the second reagent comprises        a pH-adjustment reagent for increasing the pH of the slurry, and        the method further comprises flocculating the slurry after        mixing in the second tank and before recycling the slurry.    -   11. A method of treating a gas well hydrofracture flowback        and/or production wastewater (production wastewater),        comprising:        -   contacting a production wastewater comprising barium, with a            source of sulfate ions, in a first tank and under conditions            to precipitate barium sulfate;        -   precipitating barium sulfate from the production wastewater            in the first tank to form a slurry of precipitated barium            sulfate and a wastewater brine, the wastewater brine            comprising sodium, magnesium, strontium, and calcium            chlorides;        -   moving the slurry to a second tank;        -   mixing the slurry with a pH-adjusting reagent in the second            tank to increase the pH of the slurry;        -   removing the precipitated barium sulfate from the slurry to            form a separated wastewater brine;        -   moving the separated wastewater brine to a third tank;        -   contacting the separated wastewater brine with a source of            sulfate ions in the third tank and under conditions to            precipitate strontium sulfate; and        -   precipitating strontium sulfate from the separated            wastewater brine.    -   12. The method of any preceding or following        embodiment/feature/aspect, further comprising:        -   removing precipitated strontium sulfate from the separated            wastewater brine to form a refined wastewater brine; and        -   evaporating the refined wastewater brine to form water and            evaporation products, the evaporation products comprising            crystalline sodium chloride.    -   13. The method of any preceding or following        embodiment/feature/aspect, further comprising adjusting the pH        of the refined wastewater brine to be between 6.5 and 7.5,        before the evaporating.    -   14. The method of any preceding or following        embodiment/feature/aspect, further comprising flocculating the        slurry after mixing with the pH-adjusting reagent and before        removing the precipitated barium sulfate.    -   15. The method of any preceding or following        embodiment/feature/aspect, wherein the contacting comprises:        -   adding from about 100% to about 150% of a stoichiometrically            equivalent amount of sulfate ions to the first tank, based            on the amount of barium ions in the first tank.    -   16. The method of any preceding or following        embodiment/feature/aspect, further comprising:        -   moving the refined wastewater brine to a third tank;        -   adding from about 100% to about 150% of a stoichiometrically            equivalent amount of sulfate ions to the third tank, based            on the amount of strontium ions in the third tank; and        -   precipitating strontium sulfate in the third tank.    -   17. The method of any preceding or following        embodiment/feature/aspect, further comprising adding potassium        permanganate to the first tank while contacting the production        wastewater with the source of sulfate ions.    -   18. A method of treating a gas well hydrofracture flowback        and/or production wastewater (production wastewater),        comprising:        -   contacting a production wastewater comprising barium, with a            source of sulfate ions, in a first tank and under conditions            to precipitate barium sulfate;        -   precipitating barium sulfate from the production wastewater            in the first tank to form a slurry of precipitated barium            sulfate and a wastewater brine, the wastewater brine            comprising sodium, magnesium, strontium, and calcium            chlorides;        -   moving the slurry to a second tank;        -   mixing the slurry with a pH-adjusting reagent in the second            tank to increase the pH of the slurry;        -   removing the precipitated barium sulfate from the slurry, in            the form of a barite sludge;        -   concentrating the barite sludge;        -   stabilizing the barite sludge; and        -   increasing the pH of the barite sludge.    -   19. The method of any preceding or following        embodiment/feature/aspect, wherein the concentrating comprises        concentrating the barite sludge in a thickener.    -   20. The method of any preceding or following        embodiment/feature/aspect, wherein the stabilizing comprises        adding calcium lignin sulfonate, polyacrylate, another polymer,        or a combination thereof, to the barite sludge.    -   21. The method of any preceding or following        embodiment/feature/aspect, wherein, after the concentrating, the        stabilizing, and the increasing the pH, the resulting barite        sludge is in the form of a liquid slurry, and the method further        comprises packaging the liquid slurry in a storage tank.

The present invention can include any combination of these variousfeatures or embodiments above and/or below as set-forth in the completesentences and/or in individual clauses taken therefrom. Any combinationof disclosed features herein is considered part of the present inventionand no limitation is intended with respect to combinable features.

The entire contents of all references cited in this disclosure areincorporated herein in their entireties, by reference. Further, when anamount, concentration, or other value or parameter is given as either arange, preferred range, or a list of upper preferable values and lowerpreferable values, this is to be understood as specifically disclosingall ranges formed from any pair of any upper range limit or preferredvalue and any lower range limit or preferred value, regardless ofwhether such ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

Other embodiments of the present teachings will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present teachings disclosed herein. It is intended thatthe present specification and examples be considered exemplary only.

What is claimed is:
 1. A method of treating a gas well hydrofractureflowback and/or production wastewater (production wastewater),comprising: contacting a production wastewater comprising barium, with asource of sulfate ions, in a first tank and under conditions toprecipitate barium sulfate; precipitating barium sulfate from theproduction wastewater in the first tank to form a slurry of precipitatedbarium sulfate and a wastewater brine, the wastewater brine comprisingsodium, magnesium, strontium, and calcium chlorides; moving the slurryto a second tank; mixing the slurry with a second reagent in the secondtank; recycling the slurry to the first tank and repeating theprecipitating, moving, and mixing to form a refined wastewater brine;and evaporating the refined wastewater brine to form water andevaporation products, the evaporation products comprising crystallinesodium chloride.
 2. The method of claim 1, wherein the evaporatingfurther comprises forming a liquor comprising from about 25% by weightto about 60% by weight calcium chloride based on the total weight of theliquor.
 3. The method of claim 2, further comprising filtering theevaporation product to form a retentate comprising crystalline sodiumchloride, and a filtrate comprising the liquor; washing the retentatewith saturated sodium chloride brine; and drying the washed retentate.4. The method of claim 3, further comprising cooling the evaporationproduct prior to the filtering.
 5. The method of claim 1, furthercomprising measuring the specific gravity of the filtrate.
 6. The methodof claim 1, further comprising: moving the refined wastewater brine to athird tank; adding from about 100% to about 150% of a stoichiometricallyequivalent amount of sulfate ions to the third tank, based on the amountof strontium ions in the third tank; and precipitating strontium sulfatein the third tank.
 7. The method of claim 6, further comprisingrecovering and drying the precipitated strontium sulfate.
 8. The methodof claim 1, wherein the contacting comprises: adding from about 100% toabout 150% of a stoichiometrically equivalent amount of sulfate ions tothe first tank, based on the amount of barium ions in the first tank. 9.The method of claim 1, further comprising adjusting the pH of therefined wastewater brine to be between 6.5 and 7.5, before theevaporating.
 10. The method of claim 1, wherein the second reagentcomprises a pH-adjustment reagent for increasing the pH of the slurry,and the method further comprises flocculating the slurry after mixing inthe second tank and before recycling the slurry.
 11. A method oftreating a gas well hydrofracture flowback and/or production wastewater(production wastewater), comprising: contacting a production wastewatercomprising barium, with a source of sulfate ions, in a first tank andunder conditions to precipitate barium sulfate; precipitating bariumsulfate from the production wastewater in the first tank to form aslurry of precipitated barium sulfate and a wastewater brine, thewastewater brine comprising sodium, magnesium, strontium, and calciumchlorides; moving the slurry to a second tank; mixing the slurry with apH-adjusting reagent in the second tank to increase the pH of theslurry; removing the precipitated barium sulfate from the slurry to forma separated wastewater brine; moving the separated wastewater brine to athird tank; contacting the separated wastewater brine with a source ofsulfate ions in the third tank and under conditions to precipitatestrontium sulfate; and precipitating strontium sulfate from theseparated wastewater brine.
 12. The method of claim 11, furthercomprising: removing precipitated strontium sulfate from the separatedwastewater brine to form a refined wastewater brine; and evaporating therefined wastewater brine to form water and evaporation products, theevaporation products comprising crystalline sodium chloride.
 13. Themethod of claim 12, further comprising adjusting the pH of the refinedwastewater brine to be between 6.5 and 7.5, before the evaporating. 14.The method of claim 11, further comprising flocculating the slurry aftermixing with the pH-adjusting reagent and before removing theprecipitated barium sulfate.
 15. The method of claim 11, wherein thecontacting comprises: adding from about 100% to about 150% of astoichiometrically equivalent amount of sulfate ions to the first tank,based on the amount of barium ions in the first tank.
 16. The method ofclaim 11, further comprising: moving the refined wastewater brine to athird tank; adding from about 100% to about 150% of a stoichiometricallyequivalent amount of sulfate ions to the third tank, based on the amountof strontium ions in the third tank; and precipitating strontium sulfatein the third tank.
 17. The method of claim 11, further comprising addingpotassium permanganate to the first tank while contacting the productionwastewater with the source of sulfate ions.
 18. A method of treating agas well hydrofracture flowback and/or production wastewater (productionwastewater), comprising: contacting a production wastewater comprisingbarium, with a source of sulfate ions, in a first tank and underconditions to precipitate barium sulfate; precipitating barium sulfatefrom the production wastewater in the first tank to form a slurry ofprecipitated barium sulfate and a wastewater brine, the wastewater brinecomprising sodium, magnesium, strontium, and calcium chlorides; movingthe slurry to a second tank; mixing the slurry with a pH-adjustingreagent in the second tank to increase the pH of the slurry; removingthe precipitated barium sulfate from the slurry, in the form of a baritesludge; concentrating the barite sludge; stabilizing the barite sludge;and increasing the pH of the barite sludge.
 19. The method of claim 18,wherein the concentrating comprises concentrating the barite sludge in athickener.
 20. The method of claim 18, wherein the stabilizing comprisesadding calcium lignin sulfonate, polyacrylate, another polymer, or acombination thereof, to the barite sludge.
 21. The method of claim 18,wherein, after the concentrating, the stabilizing, and the increasingthe pH, the resulting barite sludge is in the form of a liquid slurry,and the method further comprises packaging the liquid slurry in astorage tank.